This is an initial submission in response to program announcement PAR-01-056. The Principal investigator (David Sarwer, Ph.D.) is currently in the third year of a K23 Mentored Patient-Oriented Research Career Development Award (K23-DK60023) from NIDDK. One of the studies supported by that award is an investigation of the psychosocial status of bariatric surgery patients. The proposed Study in this application builds upon preliminary findings from that study and is designed to generate pilot data for a subsequent R01 application. Presently, 6.3 % of women and 3.1% of men suffer from extreme obesity, defined as a body mass index (BMI) >= 40 kg/m 2. For many of these individuals, bariatric surgery is the most efficacious intervention. Patients typically lose 40-60% of their excess body weight and frequently experience improvements in obesity-related co-morbidities. Surprisingly, there have been few studies of postoperative eating behavior and its relationship to weight loss, as well as of untoward events such as nausea, vomiting, and dumping. Several studies, including preliminary data from our ongoing investigation, have suggested that patients who adhere poorly to the postoperative diet experience smaller weight losses. The present study will investigate weight loss, caloric and macronutrient intake, eating behavior, nausea, vomiting, and dumping in 100 patients who undergo bariatric surgery. Fifty individuals will receive biweekly dietary counseling for the first 16 postoperative weeks. Fifty will receive standard post-operative care, which involves no postoperative dietary counseling but access to a monthly support group and on-line chat room. We predict that at 4, 6, 12, and 18 months postoperatively patients who receive intensive dietary counseling will experience larger weight losses and better dietary adherence, as well as less frequent nausea, vomiting, and dumping, as compared to those who receive standard care. The inclusion of dietary counseling during the postoperative period is an innovation in the treatment of bariatric surgery patients. Results of this study could have a significant impact on the postoperative care of these individuals.